Your memory use is between my Desktop and Laptop. I will assume you are using a laptop, so your Hardware Reserved should be higher. If you had a desktop with a discreet video card, it would be low.
You Modified memory is higher than either one of my systems. But I have nothing open except Firefox and that appears to be something like Page files.
To illustrate how difficult it might be to find, your svchost.exe (LocalServiceNetworkRestricted) is quite a bit higher than mine. But the Process ID (PID) includes 5 functions, including Audio and Security.
Your "In Use" seems reasonable, but the only way to tell what is using is to add up the numbers. To do add the numbers when they are changing, I like to use the snipping tool to take a picture and then add. You might start taking a picture during different system states to see if there is some large change. If one thing was causing an 800 MB memory usage, it should be easy to find. If it is a bunch of small things, it may not be so obvious.
Your Steam entry shows about 100 MB higher than mine, but no game is currently running.
Can I ask you what happened to get your attention? Maybe you happen to catch it before during a time of minimal use.